Anexelekto (also referred to as “AXL”, “UFO”, “ARK”, or “TYRO7”; hereinafter referred to as “AXL”), which has been cloned from patients with chronic myeloid leukemia, is an oncogene capable of transforming mouse NIH3T3 cells when highly expressed (Non-patent Documents 1 and 2). AXL protein is a 140-kDa receptor tyrosine kinase (Non-patent Document 3), and is said to be responsible for signal transduction to downstream molecules through its autophosphorylation, which occurs after it binds to the ligand Gas6 (growth arrest specific gene 6) (Non-patent Document 4). Receptor tyrosine kinases, such as Sky, Mer, and AXL, are known as receptor tyrosine kinases with Gas6 as a ligand (Non-patent Document 5).
AXL is presumed to have molecular functions involved in cell growth enhancement, suppression of apoptosis, cell migration, and cell adhesion. Experimentally observed phenomena in cells treated with Gas6 protein support this presumption. Reported experimental results include its suppression of cell death and its enhancement of cell growth in rat vascular smooth muscle (Non-patent Documents 6 and 7), the acceleration of cell growth and the suppression of cell death after serum starvation in mouse NIH3T3 cells (Non-patent Documents 8 and 9), the promotion of cell growth in mouse cardiac fibroblasts (Non-patent Document 10), the enhancement of cell growth in human prostate cancer cells (Non-patent Document 11), the enhancement of cell growth and infiltration and the suppression of cell death in human gastric carcinoma cells (Non-patent Document 12), the enhancement of the migration ability of human and rat vascular smooth muscle cells (Non-patent Document 13), the enhancement of the cell migration ability of mouse neurons (Non-patent Document 14), and the aggregation of cells highly expressing mouse AXL (Non-patent Document 15).
Similarly, PI3K-Akt pathway and MAPK pathway are said to function as downstream pathways of the signal transduction mediated by AXL based on molecular analyses of intracellular signals after treatment with Gas6 (Non-patent Document 5). An analysis with a yeast two-hybrid method using an AXL intracellular region as the bait confirmed the direct molecular interactions with these downstream pathways. As a result, GrbB2/PI3K/p55γ/SOCS-1/NcK2/RanBP2/C1-TEN were identified (Non-patent Document 16). The interactions of these molecules suggest the presence of intracellular signal transduction pathways as downstream from the AXL signal. Furthermore, the observed interactions support the presumption that AXL functions in cell growth enhancement, the suppression of apoptosis, cell migration, and cell adhesion. AXL has also been identified as a gene highly expressed when TNFα-induced cell death of mouse fibroblasts is suppressed by IL-15. The suppression of TNFα-induced cell death was abolished by suppressing AXL expression, and the phosphorylation of IL-15 receptors and AXL was enhanced by treatment with IL-15. These experimental findings also suggest that signal transduction is mediated by the complex of AXL and IL-15 receptor (Non-patent Document 17).
Tumorigenicity of nude mice has been reported to dissipate as a result of inhibiting Gas6-dependent phosphorylation of AXL in human glioma lines overexpressing the AXL dominant negative form (Non-patent Document 18). However, there have been no reports or suggestions and remain unclear whether any anti-AXL antibody which inhibits phosphorylation exists.
AXL is a single-pass transmembrane receptor tyrosine kinase, and the extracellular region is composed of two immunoglobulin-like domains (referred to as IgD1 and IgD2) and two fibronectin type III domains (referred to as FND1 and FND2) from the N-terminal side (Non-patent Document 3). Although FND is known to be expressed in molecules such as neural cell adhesion molecules and nephrins involved in intercellular adhesion, detailed functions of FND in AXL are unclear (Non-patent Document 19).
AXL has been identified as an oncogene that retains an inherent ability to transform cells, and has been studied as a carcinogenesis-related molecule. Many analyses of AXL expression have been reported on the protein and mRNA. The high expression of AXL protein has been reported in human tumor tissues and tumor cells, including lung cancer (Non-patent Document 20), breast cancer (Non-patent Document 21), ovarian cancer (Non-patent Document 22), thyroid cancer (Non-patent Document 23), melanoma (Non-patent Document 23), renal cancer (Non-patent Document 24), gastric cancer (Non-patent Document 12), and glioma (Non-patent Document 25). Furthermore, the high expression of AXL protein is suggested by high levels of AXL mRNA in esophageal cancer (Non-patent Document 26), colon cancer (Non-patent Document 27), and acute myeloid leukemia (Non-patent Document 28). There are also reports of the inhibition of lumen formation via the suppression of AXL by RNAi in HUVEC (Non-patent Document 29), the reduced tumor-forming ability of human breast cancer cells in mice resulting from the constitutive suppression of AXL (Non-patent Document 29), and the reduced tumor-forming ability of human glioma cells in mice resulting from the constitutive high expression of dominant negative mutants (Non-patent Document 25). The involvement of AXL molecular functions in tumor growth is strongly suggested.
Polyclonal antibodies to the extracellular domain of AXL have been reported to have a migration inhibitory action on highly invasive breast cancer cell lines (Patent Document 1). However, non-clinical studies showed that drugs demonstrating cancer-cell-migration-inhibitory action do not necessarily demonstrate antitumor activity. For example, matrix metalloproteinase (hereinafter abbreviated to “MMP”) has been known to promote tumor infiltration and migration. Thus, attention has been focused on various matrix metalloproteinase inhibitors that inhibit the enzyme activity of MMP, and clinical studies have been conducted on various pharmaceutical agents such as Batimastat, Marimastat, and Prinomastat. However, antitumor effects have not been observed in the clinical trials (Non-patent Document 30).
Accordingly, there have been no reports or suggestions and it remains unknown whether anti-AXL antibodies have antitumor effects particularly in vivo, whether they can suppress angiogenesis, and whether they can suppress cancer.    Patent Document 1: WO 2004/008147    Non-patent Document 1: Liu, et al., Proc. Natl Acad. Sci. U.S.A. (1988) 85, 1952-6    Non-patent Document 2: Janssen, et al., Oncogene (1991) 6, 2113-20    Non-patent Document 3: O'Bryan, et al., Mol. Cell. Biol. (1991) 11, 5016-31    Non-patent Document 4: Varnum, et al., Nature (1995) 373, 623-626    Non-patent Document 5: Hafizi, et al., FEBS J. (2006) 273, 5231-5244    Non-patent Document 6: Nakano, et al., FEBS Lett. (1996) 387, 78-80    Non-patent Document 7: Nakano, et al., J. Biol. Chem. (1995) 270, 5702-5    Non-patent Document 8: Goruppi, et al., Mol. Cell. Biol. (1997) 17, 4442-53    Non-patent Document 9: Bellosta, et al., Oncogene (1997) 15, 2387-97    Non-patent Document 10: Stenhoff, et al., Biochem. Biophys. Res. Commun. (2004) 319, 871-8    Non-patent Document 11: Sainaghi, et al., J. Cell. Physiol. (2005) 204, 36-44    Non-patent Document 12: Sawabu, et al., Mol. Carcinog. (2007) 46, 155-164    Non-patent Document 13: Fridell, et al., J. Biol. Chem. (1998) 273, 7123-6    Non-patent Document 14: Allen, et al., Mol. Cell. Biol. (2002) 22, 599-613    Non-patent Document 15: McCloskey, et al., J. Biol. Chem. (1997) 272, 23285-91    Non-patent Document 16: Hafizi, et al., Biochem. Biophys. Res. Commun. (2002) 299, 793-800    Non-patent Document 17: Budagian et al., Embo J. (2005) 24, 4260-70    Non-patent Document 18: Vajkoczy P et al., Proc. Natl Acad. Sci. U.S.A. (2006) 103, 5799-804    Non-patent Document 19: Yamagata et al., Curr. Opin. Cell. Biol. (2003) 15, 621-632    Non-patent Document 20: Shieh, et al., Neoplasia (2005) 7, 1058-1064    Non-patent Document 21: Meric, et al., Clin. Cancer Res. (2002) 8, 361-367    Non-patent Document 22: Sun, et al., Oncology (2004) 66, 450-457    Non-patent Document 23: Ito, et al., Thyroid (2002) 12, 971-975    Non-patent Document 24: Chung, et al., DNA Cell Biol. (2003) 22, 533-540    Non-patent Document 25: Vajkoczy, et al., Proc. Natl. Acad. Sci. U.S.A. (2006) 103, 5799-804    Non-patent Document 26: Nemoto, et al., Pathobiology (1997) 65, 195-203    Non-patent Document 27: Craven, et al., Int. J. Cancer (1995) 60, 791-797    Non-patent Document 28: Neubauer, et al., Blood (1994) 84, 1931-1941    Non-patent Document 29: Holland, et al., Cancer Res. (2005) 65, 9294-9303    Non-patent Document 30: Pavlaki et al., Cancer Metastasis Rev. (2003) 22, 177-203